Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$236.41	5.854%	$250.2494	$250.25	$250.25	$250.20
Purchase #2	$24.83	11.847%	$27.7716	$27.77	$27.75	$27.80
Purchase #3	$78.60	8.684%	$85.4256	$85.43	$85.45	$85.40
Purchase #4	$156.85	6.461%	$166.9841	$166.98	$167.00	$167.00
Purchase #5	$219.97	6.782%	$234.8884	$234.89	$234.90	$234.90
Purchase #6	$19.96	6.594%	$21.2762	$21.28	$21.30	$21.30
Purchase #7	$129.63	9.423%	$141.845	$141.85	$141.85	$141.80
7 purchase totals =	$866.25		$928.4403	$928.45	$928.50	$928.40